File Code: Date: June 23, 2014

Subject: Lake and Wetlands Crossings on West end of Hematite Nature Trail

To: Darrin Samborski, Environmental Education Specialist and William Ryan, Trails

Specialist at The Land Between the Lakes

On May 20 and 21, 2014, Jerry Barrow, a 2014 retired US Forest Service Civil Engineer with

USFS Trails Unlimited Enterprise Team, walked the Hematite Nature Trail with Darrin and Bill

to review the wetlands crossing structures located on the western end of Hematite Lake. The

group also reviewed an existing elevated lake viewing earth platform. This had a failing low

height retaining wall on the front side toward the lake. The existing nature trail, structures

and the wetlands crossings were constructed by the Tennessee Valley Authority, whom

originally managed the LBL lands, some 20 plus years ago. The main objectives of the group

walk was to review the existing structures, the wetlands crossing boardwalks, their physical

conditions, discuss alternative construction techniques and various structures types that

could be constructed to replace the aging structures. The secondary objective was to do

more research into the various construction techniques for the crossings and develop some

estimated construction costs associated with the different techniques. These would consider

the low impacts to the wetlands soils, the engineering/installation methods, and the

aesthetics of the structures on the landscape. These construction techniques and their

estimates are to be provided so that the LBL Management Staff can use them as guide to

make future structures replacement funding request. As such, I reviewed four boardwalk

construction technique options for the lower deck height wetlands crossings sections, and the

light weight Fiber Reinforced Polymer (FRP) trail bridge structure option for the replacement

of the existing 60 ft. and 90 ft. trail bridges over the drainage channels that inflow into

Hematite Lake.

I was provided a GPS Hematite Trail map, access too and copies of the existing trail bridge

maintenance records, and information of the top elevation of Hematite Dam of 372 ft. The

group walked the wetlands and bridge crossings three times over the two field days. Bill

stated that approximately 300-350 LF of the plastic plank boardwalk set on the ground on

the southwest side of the wetlands crossing could remain in place because of their

satisfactory condition at this time. Rough measurements were made of the remaining

boardwalk and bridges. For my estimates, utilizing these approximate field measurements, I

made assumptions of 750 LF of elevated boardwalk and two existing bridges, a 60 ft. and 90

ft. that have 10 ft. of approaches per bridge end.

I applied engineering experience and trail bridge construction knowledge as I researched the

construction techniques. I contacted five fabrication vendors to get updated material costs.

With this information and the Trails Unlimited cost guide I developed the cost estimates for

the Hematite Trail crossings. In three of the four boardwalk techniques I incorporated the

vertical steel helical supports. I believe this is the recommended technique to increase the

structures lifespan and durability rather than installing wood timber supports in the water

and saturated soils. These methods and their associated costs are:

1. 60 inch total width pressure treated (PT) timber boardwalk with 7 inch high side

curbing. The 4 x 4 curbing with scrubber blocks provides 5 ft. 5 inches of clear

width walking tread. The timber deck is set on 10 ft. span of three – 4 x 14 timber

stringers connected to timber headers that are set in HDG steel saddles and helical

vertical supports. A typical helical with a 12 inch disc head diameter would be

installed (mechanically screwed) 5 ft. to 10 ft. into the ground with hydraulic torque

head that is attached to a mini excavator’s hydraulic boom. The helical supports

have very minimal ground disturbance. Helical supports are similar to giant screws

with support saddles for header beams. The structure will meet FS standards and

be rated to allow small mechanized equipment to cross the west lake end for

maintenance purposes. Estimated purchase and installation cost for 750 ft.

of boardwalk is $309,702.

(As a note, the estimates for all options include some cost to remove the existing

structures, site prep and layout, mobilization variables)

Figure 1: 6 ft. wide x 330 ft. long timber boardwalk elevated over wetlands on the

Oconee National Forest, Georgia constructed 2008. Constructed during drought.

2. Fiber Reinforced Polymer (FRP) beams with a 3 x 12 timber deck boardwalk system

and timber curbing. The 12 inch FRP beams are attached to wood header beams

set in steel saddle supports connected to the steel helical vertical supports in the

soil. The fiberglass beams are lightweight, very strong and can be used to span

15-25 ft., and therefore require fewer boardwalk foundation supports. The fewer

supports would be less restrictive to surface water flow that trap debris on the

supports. The objective is to set the top deck elevation 30 inches above the water

surface at high water flows underneath the structure. This should not require

handrails. I am estimating 30-36 inches max height above the water surface at full

pool.

Estimated purchase and the installation cost for 750 LF of the FRP

boardwalk with a standard PT timber deck is $333,606.00. The vendor

quoted that for an additional $37,500 he can supply Trimax decking. He delivers a

lot of this material to the US Park Service for walkway decking. Trimax is a

structural lumber made of HDPE resins and recycled plastic products. The material

is resistant to moisture, fungi, borers, and will not rot, splinter, check or stain. It is

low maintenance because it requires no scrubbing, staining, or power washing. It

looks like and cuts like wood. Therefore, the estimate with the Trimax

decking is $371,106.00

Figure 2: Example of fiber glass (FRP) stringers with timber deck and low curb for

pedestrian walkway

Figure 3: Steel Helical and walkway bracket system for timber and or FRP

beam support.

3. A third option is the precast concrete PermaTrak boardwalk system

(www.permatrak.com). This boardwalk system is composed of precast concrete

stringers, decking, curbing and supports. I recommend the boardwalk system be

60 inch wide, but it could be 48 inches in width, with a 4 inch wide concrete curb

on each side. This is a very durable and low maintenance boardwalk system. Its

main drawback would be the mobilization and placement of the heavy concrete

pieces. Heavier equipment would be required for installation vs. the other methods,

resulting in a greater chance for ground disturbance. Because of the soft soils in

the Hematite Lake waters, the vendor recommends that vertical steel helical piles

or a large vertical H piles with flat top plate steel to support concrete beams be

used. It would be much more difficult to move the concrete pieces into place on

the lake, unless the project work areas were completely dry and firm for heavier

equipment to operate and construct the boardwalk. The pathway ground needs to

be tested for it soil bearing capacity by a testing company. It is low on my list of

recommendations for this location. The estimated cost for purchase and

installation of 750 LF is approximately $316,000.00. It could cost more

because of operation difficulty with the heavier equipment and materials.

A crew may have to build off the platform to move the construction

process ahead.

Figure 4: PermaTrak precast concrete boardwalk system

4. The last boardwalk system option that I discussed with Darrin and Bill was a

prefab-portable, low profile boardwalk system, with galvanized steel support

frames, on adjustable support pad foundations as produced by Wickcraft Company,

Inc. of Madison, Wisconsin. The prefabricated boardwalk has a design load rating of

100 lbs. per sq. foot to meet current standards. This boardwalk system would not

require any excavation of the native soil, other than the leveling for the larger

support pads in the soft Hematite Lake soils. It will not alter the wetlands drainage

flow patterns. The steel frame system supports will require some trimming or

removal of the top vegetative layer by the bearing pads. The Wickcraft Company

boardwalk system has 10 ft. spans between supports with load bearing pads that

sit on the soil surface at each support. A Manta Ray earth anchor can be installed

on a leg support, per unit span, as a precaution against lateral movement by water

flows or possible high winds that could create uplift reaction forces. The deck

panels come somewhat preassembled, so this type of boardwalk system should be

the fastest to install. The estimated cost of the standard PT timber decking

Wickcraft boardwalk system, purchased and installed is $193,665 for 750

LF. The Wickcraft System with Bedford Technology HDPE plastic

boardwalk decking surface has an estimated cost of $255,945. The HDPE

decking would provide a much longer life span and the low maintenance

requirements for the wetlands boardwalk crossings.

Figure 5: Wickcraft steel frame and timber deck boardwalk system

Figure 6: Wickcraft steel frame and HDPE deck and curb boardwalk system with

the wide support pads for soft soils.

Trail Bridges:

There are two main bridge structure crossings on the western side of the Hematite Trail. One

is Trail Bridge HE-BR1. This is a two – 30 ft. steel girder spans connected together to create

a 60 ft. bridge structure with boardwalk approaches. The other is Trail Bridge HE-BR2. This

is a two – 45 ft. steel joist spans connected together to create a 90 ft. bridge structure. Both

of these bridges were inspected by Engineers in June 2013 and rated as in “Fair Condition”.

Figure 7: Existing Trail Bridge HE-BR1. Picture taken upstream of bridge.

Figure 8: Trail Bridge HE-BR1. Viewing West. Upstream side of bridge is right.

Replacement options for the bridge structures were reviewed for HE-BR1 and BR2. These

were timber, timber glulam beams, steel, and Fiber Reinforced Polymer (FRP) trail bridges.

The timber, timber glulam beams, and the steel bridges would be extremely heavy and

difficult to move and erect for the long spans required in the existing wetlands sites. These

type of bridges would require much larger lifting equipment to move the heavy timber or

steel bridge stringers and or glulam bridge panels onto larger constructed bridge abutments

on the narrow strip of dry land in the wetlands. Access is a major problem. Therefore, the

Fiber Reinforced Polymer (FRP) bridges are the recommended material structures for both

the two - 30 LF long spans and the two – 45 LF long span crossings.

Typically the structures are 6 ft. wide with 42 inch high truss/handrail system for pedestrian

use. See example in Figure 10 and 11. The FRP bridges are broken down into components

that are lightweight to move and construct. They provide a very strong structure that meets

the load requirements specified by the Forest Service. The FRP bridges are low maintenance

structures and they blend in with the landscape because of the smaller structural members

that are required. The colors of green or brown blend in well with the native forest

environment. Smaller equipment can be used to move the bridge materials to the site,

resulting in less ground impacts. The construction team can erect the bridge across the wide

drainage channel utilizing scaffoldings, or perhaps build the new bridge parallel to the

existing bridge structure so as to use it as a working platform. The old bridge structures

would be removed after the new bridge completion.

During the May field review, the question was presented by Bill and Darrin, could the two –

30 ft. spans bridge structure be replaced with the similar kind boardwalk system that is being

considered for the wetlands crossing? At present, there have not been any hydrology studies

of the Hematite Lake drainages in the recent years by the Forest Service. No one knows

where available records from TVA of the site may be found for predicted water flows. My

recommendations are being made from the May 2014 field trip observations and my personal

trail bridge engineering experience.

I believe that this duel span bridge crossing could be converted into the similar boardwalk

system. Two – 30 ft. span Fiber Reinforced Polymer bridges, with non-retardant structural

members, would cost $36,500 just for the bridges delivered to LBL. Estimated total

installed cost with abutment is $98,500. The same bridges with fire retardant members

would cost $42,500 for a total installed cost with the abutments of $104,500. I do

not believe the lake site location warrants the fire retardant FRP members. This would be a

LBL Management and Engineering decision.

If 3 sections of 20 ft. span boardwalk and curb system were substituted for the two span

bridge by utilizing 12 inch deep FRP beams, with a Trimax deck and curbing on helical

foundations, the estimated material cost for the structure is $23,348 and installed

total is estimated $34,948. This is without a handrail system, only deck curbing. A

significant cost savings.

The recommendation to survey the stream bottom cross section profile at this site. It must

be determined if the new structure can be set so as to allow the top deck elevation to be no

more than 30 inches above the water surface and still allow high drainage flows into

Hematite Lake without trapping debris. This deck height would not require handrails on the

boardwalks, but only the walkway side curbing. Since the answer is not known, for funding

request purposes one should use the $98,500 for the two – 30 ft. bridges in the estimate.

Figure 9: Existing Trail Bridge HE-BR2. Two - 45 ft. Spans with center pier.

As shown in Figure 9, the 90 ft. trail bridge HE-BR2 consists of two – 45 ft. steel joist truss

bridges with a plastic composite deck. The recommended available options: 1.) replace

existing with two – 45 ft. FRP bridges on a new center stream precast concrete abutment for

a total estimated install cost of $150,200.

2.) Replace the two 45 ft. bridge sections with one – single span 6 ft. wide x 90 ft.

FRP trail bridge for a total estimated construction cost of $173,700. This eliminates

the construction of a center pier, but the structural stringer members are larger and there

are several bridge splices. The cost would be somewhat contingent on whether the lake

could be drained down to allow the ground around the bridge abutment/piers to dry out and

stabilize for several months for larger machines to have access to lift the bigger bridge

components. Otherwise, scaffolding would need to be erected to support the construction of

the bridge or the engineering and construction team could study if it is possible to use the

existing bridge as a working platform until the project is completed. It would then be

removed.

Figure 10. All terrain crane setting a 75 ft. FRP bridge frame that was put together

on dry ground and lifted onto the abutments in Okefenokee NWR, Georgia.

Figure 11: Completed hike and bike 75 Ft. FRP Bridge at Okefenokee NWF

Lake and Wildlife Viewing Platform Retaining Wall Repairs

An existing lake viewing platform, composed of retained native soil, on a slope of the

northern side of the Hematite Nature Trail was re-assessed by the group. It has

approximately 29 LF of existing handrail with a 2 ft. high timber retaining wall on the front

side facing the lake. The timbers are decaying and should to be replaced.

I looked at several options to replace the front retaining wall. 1) Lock and Load precast

concrete retaining wall system. I have used these for a horse trail bridge on National Forest

in South Carolina. The nearest fabricating plant to LBL is in Grandview, Missouri. Upon

receiving updated material cost, haul cost and the small volume required, and I re-evaluated

the installation process I decided this is not the best fit for the dollars at the location. The

existing native hillside platform ground would need to be excavated deeper to install the

counter-weight components of the precast concrete face wall structure. This is more ground

disturbance than I believe warrants the location. The small amount of concrete units

required for this wall repair are heavy and therefore expensive to ship.

2). It is my recommendation to use the Sutter Retaining Wall system. This is the same steel

H pile and timber lag wall with a steel tie back earth anchor system that was incorporated

into 150 LF of the Central Hardwood Trail adjacent to the 68/80 Highway. I believe the wall

system can be installed just in the front of the existing timber wall and lengthened to tie into

the back hillside better. Once the Sutter wall is installed, the existing decaying timbers can

be removed and the front wall area backfilled with drainage stone against the back side of

the Sutter Wall system. I made the assumption and estimated 40 LF of wall to cover the

additional end walls distance to tie back to natural ground since I did not have an

engineering site survey. The existing wall is approximately 2 – 2.5 ft. high. The Sutter wall

could be raised to 3 ft. and the platform surfaced with new stone and new handrail. The

viewing platform would also be connected back into the proposed relocated Hematite trail

section on a more sustainable grade. It is estimated for the USFS Trails Unlimited

Enterprise Team to install the Sutter H pile, earth anchors, timber lag wall and

handrail would be approximately $18,000.

Figure 12 above: Sutter Wall under construction. Figure 13 below: nearly

completed wall system on the Central Hardwood Trail, Land Between The Lakes

Forest Wildlife Viewing Blind – Proposed Wall on South Side Hematite Lake Trail

The small wildlife viewing boardwalk and blind shed on the south side of Hematite Lake is

rapidly decaying and has become a safety hazard. Darrin and Bill propose removing the

existing structure. A forest wildlife viewing blind timber wall, with viewing portals at varying

heights, can be constructed on the south bank at the end of the old existing boardwalk and a

few feet from the bank edge. This wall could be approximately 12 ft. in length and 8 ft. high

with small wing-walls for lateral stability. I estimate to construct a stable wildlife viewing

blind wall structure and remove the existing hazardous boardwalk and deck shed to be

$9,500.

.

Figure 14 and Figure 15: Examples of Forest Wildlife Viewing Blind Wall

Summary of Recommendations:

Topo survey of the bridge site HE-BR2, the two – 45 ft. spans location and possibly

the two – 30 ft. span site as well. As a minimum, a center line survey of the existing

trail boardwalk with turn angles and some elevations, a few elevation shots for the

bottom of the ground adjacent to the structures to indicate water depth.

What is full pool elevation as to height of earth dam? Need LBL to provide.

A soils testing engineering firm should be contracted to perform several soil bearing

test along specific points of the boardwalk and bridge crossings (abutments). This

should be possible to do in one day, maybe two, of field work and some office work by

a testing firm I believe. Nashville, Clarksville or Paducah may have firms to perform

this work.

Boardwalk construction:

From my estimates, the cost wise and the fastest to construct choice is the Wickcraft

Boardwalk System. This would be on 10 ft. center supports using the HDPE deck

timbers and curbing for longevity. The estimate is $255,945 as compared to my

favorite selection with the FRP beams with 20 ft. spans on helical supports at

$316,000. The Wickcraft system shall require wide bearing pads be installed on the

legs of the vertical supports of the steel frames in the lake soft silt soils. Some of

these wide footings will not be covered by water, so as long as no one has aesthetic

concerns, it should be a good boardwalk system.

The top boardwalk deck elevations should be set as low as practical to the water

surface once the full pool elevation is known and the water height is determined in

potential high rain event. It would best to set that elevation at 30 inches above the

water surface so that only side curbing would be required on the boardwalk deck and

not handrail. In the event the deck elevation were to fall slightly higher, a Design

Warrant – which is a one page document, could be signed by LBL Management

allowing the deviations after considering risk factors. I do not think a handrail is

necessary with the curbing in place for this nature trail. It would distract from the

forest walking experience along the portions of the trail with handrails.

Trail Bridges:

I recommend the light weight, low maintenance, and non-retardant for fire structural

member FRP bridges. For the existing 90 ft. crossing, I would recommend the two –

45 ft. spans on a new center pre-cast concrete pier. Unless it was known that the lake

would be drained at the lake west end, and it might be totally dry and provide hard

ground at that location during construction, I might consider the single 90 ft. span

bridge. That would be very clean bridge design and not have a center pier that high

water flow traps debris against.

For the existing two – 30 ft. span crossing, I recommend the three - 20 ft. span FRP

beams with deck and curbs set at lower elevation. There are a few stream flow issues

to address if this is a possibility. Otherwise, plan on the cost of the two – 30 ft. FRP

span bridges set on a new center pier.

Elevated Viewing Platform Site above Hematite Lake:

Replace the existing decaying wood retaining structure with a Sutter Retaining Wall

system composed of steel H piles, timber lag walls and HDG steel earth anchor

tiebacks. Install an estimated 40 LF of wall and handrail. Improve trail connection at

the viewing site itself. Estimated cost $18,000.

Forest Wildlife Blind Viewing Structure:

A simple wood structure wall of approximately 12 ft. long x 8 ft. high and wing walls

for lateral stability to be anchored into the ground. A plan can be sketched for

approval. Remove the existing hazardous wood structure. Estimated cost $9,500.

If you have questions, please contact me.

USFS Trails Unlimited Civil Engineer - Retired